CN110465627A - A kind of surface layer densification internal defect ceramic core manufacturing method for hollow turbine vane hot investment casting - Google Patents

Abstract

The invention relates to a method for manufacturing a ceramic core with a dense surface layer and a loose interior used for precision casting of hollow turbine blades, which effectively solves the problems of insufficient yield of the ceramic core and difficulty in removing the core; it includes step 1: making a resin mold; adopting light curing to quickly Molding method manufacturing core resin mold; step 2: making ceramic slurry; preparing ceramic slurry for gel injection molding; step 3: making ceramic core; pouring ceramic slurry into the ceramic core resin mold; step 4 : impregnation treatment for the first time; use low-concentration silica sol to impregnate the ceramic core after calcining and degreasing; step five: second impregnation treatment; adopt high-concentration silica sol to impregnate the core; the present invention is based on light Solidified rapid prototyping technology and gel injection molding technology to manufacture ceramic core blanks, and then impregnate different concentrations of silica sol twice, and control the impregnation depth of silica sol, so as to achieve an alumina-based ceramic core with a dense surface and a porous center manufacturing.

Description

A ceramic type with dense surface and loose interior for precision casting of hollow turbine blades Core manufacturing method

technical field

The invention relates to the technical field of precision casting of hollow turbine blades, in particular to a method for manufacturing a ceramic core with dense surface layer and loose interior used for precision casting of hollow turbine blades.

Background technique

Hollow turbine blades are one of the core components of aero-engines and industrial gas turbines, which contain complex cooling channel structures. Currently, the blades are mainly shaped by the precision casting method. In order to form the cooling channel structure inside the blade by precision casting, it is necessary to prepare the ceramic core first. Alumina-based ceramic cores have excellent chemical stability in high-temperature environments, and are not easy to chemically react with molten metal, so they are widely used.

However, during the blade casting process, the molten metal will shrink when it solidifies, and the metal blade will also shrink during the cooling process after solidification. This shrinkage will be restricted by the ceramic core, causing the blade to crack easily, resulting in blade manufacturing failure. .

In addition, it is difficult to remove the alumina ceramic core after blade casting, so the removal of the aluminum-based ceramic core is also a technical problem that needs to be solved.

In order to solve this problem, US Patent 4184885, US Patent 4191720 and US Patent 4191721 proposed to manufacture ceramic cores with dense surface and loose center. The core has a dense surface and high strength, which can resist the impact of molten metal during blade casting. , thermal stress and gravity, high porosity and low strength inside the core, which is conducive to the crushing of the inside of the core during the cooling and shrinkage process of blade casting and forming, and improves the retreat of the core. In addition, the internal porosity of the core is high, which is conducive to the penetration of the core removal liquid into the core during the core removal process after the blade is cast, thereby increasing the removal rate of the core. In the method, the reactive disappearance filler C, B or Al is added to the alumina base material, and then the core is sintered in a reducing gas or an inert gas with an ultra-low oxygen content. Al low-valent oxide gas is formed in the center of the core and overflows to the surface of the core, resulting in the formation of a large number of communicating holes in the center of the core. After the gas overflows to the surface area of the core, it is oxidized to alumina and condenses in the surface area, which increases the density of the surface layer of the core. When the reactive disappearing filler is C, the chemical reactions that may exist under the hydrogen reducing atmosphere are shown in formula (1) and formula (2).

When the reactive disappearing filler is Al or B, the possible chemical reactions are shown in formulas (3)-(6).

Al ₂ O ₃ (s)+4Al(s)→3Al ₂ O(g) (3)

Al ₂ O ₃ (s)+Al(s)→3AlO(g) (4)

Al ₂ O ₃ (s)+2B(s)→Al ₂ O(g)+2BO(g) (5)

Al ₂ O ₃ (s)+B(s)→2AlO(g)+BO(g) (6)

However, this method requires the use of reducing gas or inert gas, which requires relatively high equipment.

In view of the above problems, the present invention proposes an impregnation method to manufacture an alumina-based ceramic core with a dense surface and a loose center, and the core has good yield and core removal performance.

Contents of the invention

The purpose of the present invention is to address the deficiencies of the prior art, and to provide a method for manufacturing an alumina-based ceramic core with a dense surface and a loose center, which is based on light-curing rapid prototyping technology and gel injection molding technology to manufacture ceramic core blanks body, and then impregnate different concentrations of silica sol twice, and control the impregnation depth of silica sol, so as to realize the manufacture of alumina-based ceramic core with dense surface and porous center, and solve the problem of insufficient yield of ceramic core and difficulty in core removal question.

A method for manufacturing a dense inner loose ceramic core for precision casting of hollow turbine blades, characterized in that it comprises the following steps:

Step 1: making a resin mold; using a light-curing rapid prototyping method to manufacture a resin mold for core gel injection molding;

Step 2: Make ceramic slurry; dissolve the monomeric crosslinking agent organic matter in deionized water to make a premix, then add ceramic powder to the premix and mix it by ball milling to make a ceramic slurry, and pour it into the ceramic slurry before pouring Add the initiator and catalyst and mix well again;

Step 3: Making a ceramic core; pouring the ceramic slurry with the initiator and catalyst into the resin mold in the step 1. After the ceramic slurry is solidified in situ, a ceramic core wet body is obtained, and then dried in sequence , Pre-fired and degreased to make a porous structure ceramic core;

Step 4: The first impregnation treatment; using low-concentration silica sol to impregnate the pre-fired and degreased ceramic core in the step 3, drying the core after being soaked, and then sintering after impregnation;

Step five: the second impregnation treatment; use high-concentration silica sol to impregnate the core in step four. This time, only the depth of the surface layer of the core is impregnated, and then the core is dried again, and then the second step is carried out. Sintering after the first impregnation, a ceramic core with a dense surface and a loose interior is obtained.

Preferably, in the first step, the resin mold is prepared by using a laser to quickly cure the photosensitive resin, and the resin mold can be degreased and removed by heating.

Preferably, the ceramic powder in the second step is alumina ceramic powder.

Preferably, the ceramic powder in the ceramic slurry in the step 2 accounts for 80%-88% by mass of the ceramic slurry, and the balance is deionized water and organic matter.

Preferably, the monomeric crosslinking agent organic matter in the step 2 is a mixture of acrylamide monomer and N,N'-methylenebisacrylamide in a mass ratio of (15-25): 1, and the initiator It is an aqueous solution of ammonium persulfate, and the catalyst is an aqueous solution of tetramethylethylenediamine, wherein the mass concentration of monomeric crosslinking agent organic matter in deionized water is 10% to 20%; the addition amount of initiator and catalyst is 0.5% of the mass of premixed liquid ~1% and 0.1%~1%.

Preferably, the concentration of low-concentration silica sol in the step 4 is 10%-20%, and the concentration of high-concentration silica sol is 30%-40%.

Preferably, the first impregnation in the step 4 is to impregnate the mandrel, and the depth of the second impregnation in the step 5 is 0.1-0.5 mm.

Preferably, after the first dipping in step 4 and the second dipping in step 5, the mandrel needs to be dried, and the drying temperature is 30°C-40°C.

Preferably, the sintering temperature after the first impregnation and the second impregnation in the step 4 and step 5 is 1300°C-1400°C, and the temperature is kept for 3-5h.

Compared with the prior art, the present invention has the following technical effects:

1) In the present invention, the silica sol is impregnated into the core, and the silica sol is converted into a fine particle component during the sintering process, which can react with the alumina matrix material to form a high-temperature strengthening phase mullite, thereby improving the mechanical properties of the ceramic core.

2) In the present invention, the ceramic core is impregnated twice, wherein the first time is completely soaked, and the second time is the depth of the impregnated part of the surface layer of the core, so the content of the impregnation on the surface layer of the core is relatively high, and can be produced after sintering. Core microstructure with dense surface and loose interior. The dense surface layer is beneficial to resist the thermal shock and thermal stress of the molten metal during the casting process, and the loose center is conducive to the solidification of the molten metal and the core being crushed from the inside during the cooling and shrinkage of the casting, thereby avoiding cracking of the casting.

3) After sintering, the core manufactured by the present invention has a dense surface and a loose interior. The loose porous structure inside is conducive to the core removal process of the blade after casting forming, and the core removal process enters the core depth, thereby increasing the contact area between the removal liquid and the core, and improving the core removal performance of the core.

4) Compared with the ceramic core manufacturing method of US Patent 4184885, US Patent 4191720 and US Patent 4191721, which has a dense surface and a loose center, this method does not require the use of a reducing atmosphere or an inert atmosphere, so the process is more secure and less harmful to equipment. The requirements are also lower.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention.

Fig. 2 is the SEM image of the microstructure of the ceramic core sample with dense surface and loose center produced by this method when the concentration of low-concentration silica sol is 20% and the concentration of high-concentration silica sol is 40%.

Detailed ways

The aforementioned and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of the embodiments with reference to the accompanying drawings 1 to 2 . The structural contents mentioned in the following embodiments are all based on the accompanying drawings of the description.

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings.

The present invention is a method for manufacturing an alumina-based ceramic core with a dense surface layer and a loose interior facing a hollow turbine blade, comprising the following steps:

1) Manufacture hollow turbine blade alumina-based ceramic core resin mold.

A photocuring rapid prototyping method is adopted to prepare a ceramic core resin mold with a photosensitive resin as a raw material, and the wall thickness of the resin mold is about 0.8-1.5 mm.

2) Ceramic core gel injection molding.

Dissolve the organic matter that functions as a monomer cross-linking agent in deionized water to make a premix solution, then add alumina ceramic powder to make a ceramic slurry, fully mix in a ball mill, add initiator and catalyst before pouring, and mix well , the mixing time was 40 minutes. Among them, the mass ratio of alumina ceramic particles to the slurry is 80% to 88%, and the balance is deionized water; the organic matter is acrylamide monomer, N, N'-methylenebisacrylamide according to (15-25): The mass ratio of 1 is the mixture, and the mass concentration in deionized water is 10% to 20%; the initiator and catalyst are ammonium persulfate aqueous solution and tetramethylethylenediamine aqueous solution, and the addition amounts of the two are respectively the mass of the premixed solution. 0.5% to 1% and 0.1% to 1%.

The ceramic slurry is poured into the resin mold to fill the inner cavity of the resin mold. After the ceramic slurry is solidified in situ, the ceramic core green body is prepared, and then the moisture inside the ceramic core is removed by freeze drying, and the organic matter inside the resin mold and the green body is removed by pre-firing and degreasing, so as to obtain a porous ceramic core green body.

3) Manufacture a ceramic core with a dense surface layer and a loose center.

The silica sol with a mass fraction of 20% is used to impregnate the pre-fired and degreased porous ceramic core body. After the core is completely soaked, the core is dried in an oven at 40°C, and then the core is Put it into a box-type resistance heating furnace, raise the temperature to 1350°C, and keep it warm for 3 hours; after the core is cooled with the furnace, put it into a silica sol with a mass fraction of 40%, and impregnate the surface of the core. About 0.15mm, and put the core into a 40°C oven again for drying treatment. Finally, the core after the second impregnation was placed in the box-type resistance heating furnace again, and the temperature was raised to 1350 °C, and kept for 3 hours to obtain a ceramic core with a loose center and a dense surface layer. Its microstructure is shown in Figure 2. It can be seen from the figure that there are fewer holes on the surface of the core and more holes inside, indicating that the surface is denser and the inside is looser.

In summary, the aluminum oxide-based ceramic core with a loose center and a dense surface layer manufactured by the present invention has the greatest advantage in that it can improve the yield of the core and solve the problem of cracking caused by metal shrinkage hindered by the core during the blade casting process. At the same time, the internal loose and porous structure is conducive to the core removal process to enter the depth of the core, increasing the contact area between the core removal liquid and the core material, thereby improving the core removal efficiency.

Claims (9)

1. A method for manufacturing a dense inner loose ceramic core for hollow turbine blade precision casting, characterized in that it may further comprise the steps: Step 1: making a resin mold; using a light-curing rapid prototyping method to manufacture a resin mold for core gel injection molding; Step 2: Make ceramic slurry; dissolve the monomeric crosslinking agent organic matter in deionized water to make a premix, then add ceramic powder to the premix and mix it by ball milling to make a ceramic slurry, and pour it into the ceramic slurry before pouring Add the initiator and catalyst and mix well again; Step 3: Making a ceramic core; pouring the ceramic slurry with the initiator and catalyst into the resin mold in the step 1. After the ceramic slurry is solidified in situ, a ceramic core wet body is obtained, and then dried in sequence , Pre-fired and degreased to make a porous structure ceramic core; Step 4: The first impregnation treatment; using low-concentration silica sol to impregnate the pre-fired and degreased ceramic core in the step 3, drying the core after being soaked, and then sintering after impregnation; Step five: the second impregnation treatment; use high-concentration silica sol to impregnate the core in step four. This time, only the depth of the surface layer of the core is impregnated, and then the core is dried again, and then the second step is carried out. Sintering after the first impregnation, a ceramic core with a dense surface and a loose interior is obtained. 2. A kind of manufacturing method for hollow turbine blade precision casting according to claim 1, characterized in that, the resin mold in the step 1 is prepared by laser rapid curing photosensitive resin, and the Resin molds can be removed by thermal degreasing. 3. A method for manufacturing a ceramic core with a dense surface and a loose interior for precision casting of hollow turbine blades according to claim 1, wherein the ceramic powder in said step 2 is alumina ceramic powder. 4. a kind of method for manufacturing a dense inner loose ceramic core for precision casting of hollow turbine blades according to claim 1, characterized in that the ceramic powder in the ceramic slurry in the step 2 accounts for the mass of the ceramic slurry The ratio is 80%~88%, and the balance is deionized water and organic matter. 5. A kind of manufacturing method for hollow turbine blade precision casting according to claim 1, characterized in that, in the step 2, monomeric crosslinking agent organic matter is acrylamide monomer and N, N´—Methylenebisacrylamide is a mixture prepared with a mass ratio of (15-25):1, the initiator is an aqueous solution of ammonium persulfate, and the catalyst is an aqueous solution of tetramethylethylenediamine, in which the monomer The mass concentration of the organic compound in the deionized water is 10%-20%; the addition amount of the initiator and the catalyst is respectively 0.5-1% and 0.1%-1% of the mass of the premixed liquid. 6. A method for manufacturing a hollow turbine blade precision casting with a dense surface and a loose interior ceramic core according to claim 1, wherein the concentration of low-concentration silica sol in the step 4 is 10% to 20%, The concentration of high concentration silica sol is 30%~40%. 7. A kind of method for manufacturing a dense inner loose ceramic core for precision casting of hollow turbine blades according to claim 1, characterized in that, the first impregnation in said step 4 is to impregnate the core, and the step The second impregnation depth of No. 5 is 0.1~0.5mm. 8. A method for manufacturing a hollow turbine blade precision casting with a dense surface and a loose interior ceramic core according to claim 1, characterized in that the first impregnation in step four and the second impregnation in step five Finally, the core needs to be dried, and the drying temperature is 30 ° C ~ 40 ° C. 9. A kind of manufacturing method for hollow turbine blade precision casting according to claim 1, characterized in that the first impregnation and the second impregnation in the step 4 and step 5 The sintering temperature after impregnation is 1300°C~1400°C, and the temperature is kept for 3~5h.